Plastic lenses have advantages that they are lighter and are less easily broken than glass lenses. For that reason, the plastic lenses have been used as various lenses including spectacle lenses. The plastic lenses for spectacles are generally formed by cast polymerization.
The cast polymerization is a method in which a liquid curable plastic raw material is injected into a mold and is cured by heat or energy such as ultraviolet rays to thereby obtain a molded article. A mold used in the cast polymerization is formed, for example, by causing a pair of molds to face each other at a certain spaced interval, and winding an adhesive tape around the entire peripheries of these molds.
A technique for producing a plastic lens using such a mold is disclosed, for example, in Patent Document 1. Patent Document 1 describes a liquid plastic raw material injection apparatus for forming a plastic lens. The liquid plastic raw material injection apparatus disclosed in Patent Document 1 includes an injection pipe for injecting liquid plastic raw material into a mold, and a suction pipe provided next to this injection pipe.
When the liquid plastic raw material is injected into the mold, a portion of an adhesive tape bonding the pair of molds is peeled off to make an opening, and the injection pipe is inserted into the mold. Under this condition, the tip of the suction pipe is located at the same level as that of the liquid when the mold is filled with the liquid plastic raw material. When the liquid plastic raw material is injected into the mold, the liquid surface reaches the tip of the suction pipe and blocks a suction port, thereby changing a negative pressure in the suction pipe.
When the liquid plastic raw material injection apparatus detects the change of the negative pressure in the suction pipe, it stops the injection of the liquid plastic raw material. Then, the adhesive tape is applied again, and a space (cavity) in the mold is sealed.
Furthermore, Patent Document 2 discloses a technique concerning a production method of a cured plastic product. According to the production method of a cured plastic product disclosed in Patent Document 2, an injection hole is provided in an adhesive tape wound around the entire periphery of a mold, and a liquid plastic raw material is injected through the injection hole. After the liquid plastic raw material is filled in the mold, an ultraviolet curable resin is applied to the injection hole to seal a space in the mold.